1. Field of the Invention
The present invention relates to a method and an apparatus for the MPEG video processing, and more particularly relates to a method and an apparatus to display a non-reference picture (such as the B picture in the MPEG video) by referring to a reference picture (such as the I picture or P picture in the MPEG video).
2. Description of Related Art
The standard of the compression method of motion picture expert group (hereinafter MPEG) is widely used for video compression. For example, MPEG 1 is used for video compression in VCD, and MPEG 2 is used for video compression in DVD. The bit stream of the MPEG video includes a series of I pictures (Intra-coded pictures), P pictures (forward Predictive pictures), and B pictures (Bi-directionally predictive-coded pictures). I pictures are encoded as stand-alone still image. P pictures are encoded referring to the nearest I or P pictures by forward prediction processing. B pictures are encoded referring to the nearest past and future I and P pictures by bidirectional prediction. Therefore, I pictures and P pictures will be used as reference pictures when decoding other pictures, but B pictures will not be used for decoding other pictures.
FIG. 1 illustrates a block diagram of a video reproduction apparatus 100. The video reproduction apparatus 100 is capable of reproducing video data encoded with MPEG-1 or MPEG-2 standard, and is for example, a DVD player or a VCD player. The video reproduction apparatus 100 includes a MPEG decoder 110, a memory unit 120, and a displaying unit 130. The memory unit 120 includes a number of buffer regions. The MPEG decoder 110 receives the MPEG video bit stream, decodes the encoded video bit stream, and stores the decoded pictures into the buffer regions of the memory unit 120. The displaying unit 130 reads the decoded pictures from the buffer regions of the memory unit 120, and displays the decoded pictures to a screen terminal, such as a TV monitor. Since B pictures are not referred to when decoding other pictures, it is not necessary to store a whole B picture for later reference. The size of the buffer regions for storing B pictures is generally less than the size for storing a whole B picture so as to save memory. In such design, a portion of a B picture will be displayed after the portion of the B picture is decoded, instead that the whole B picture being displayed after the whole B picture is completed decoded.
However, a B picture may be displayed abnormally if the bandwidth of the memory unit is insufficient or if the decoding is delayed due to some decoding errors. The duration of displaying errors may be short, such as 1/60 second, but the viewer can still perceive and feel uncomfortable with the errors. In addition, when the decoding of a portion of the picture is delayed, the decoding of subsequent portions may also be affected, thereby deteriorate the picture displaying quality.